Method for high-frequency tuning an electrical device, and a printed circuit board suitable therefor

ABSTRACT

The invention relates to a method for high-frequency tuning a high-frequency plug connector, comprising a printed circuit board that has both contact points for high-frequency contacts as well as contact points for insulation displacement contacts. Each contact point for the high-frequency contacts is connected to one respective contact point for the insulation displacement contacts. Capacitive couplings, which cause a near-end crosstalk, occur between the high-frequency contacts. At least one first conductor path, which is connected on only one side to a contact point of an electrical contact, is situated on the printed circuit board that, together with at least one second conductor path, which is situated on and/or in the printed circuit board, forms a capacitor. At least one frequency-dependent parameter of the device is measured, and this frequency-dependent parameter is compared to a set parameter and, according to on a difference between the two, the conductor path that is contacted on one side is partially removed or completely separated.

The invention relates to a method for RF matching of an electricalarrangement, and to a printed circuit board which is suitable for thispurpose.

EP 0 525 703 A1 discloses a plug connection for computer networks in thedomestic area, comprising a male connector part and a female connectorpart, with a device for crosstalk compensation being arranged in theplug connection, by means of which the crosstalk attenuation between thetransmission conductor loop and the reception conductor loop can beincreased. For this purpose, a printed circuit board is arranged in thefemale connector part or in the male connector part of the plugconnection between the connections for the plug-in cable and theconnections for the wiring, with the conductor routes for thetransmission and reception conductor loops being largely physicallyseparated on the printed circuit board. The devices for crosstalkcompensation are, for example, discrete components such as capacitors orcoils, which are adjustable. The known plug connection has thedisadvantage that the discrete components are relatively expensive andlarge.

DE 100 51 097 A1 discloses an electrical plug connector comprising aplug connector housing, a printed circuit board with two sets of contactelements, with the first set of contact elements being arranged on thefront face of the printed circuit board and projecting into an openingin the plug connector housing, and the second set of contact elementsbeing arranged on the rear face of the printed circuit board, and thecontact elements in the second set being in the form ofinsulation-displacement contacts, with the plug connector having a cablemanager which has an opening through it and is provided on the frontface with guides for conductors which are intended to make contact withthe insulation-displacement contacts, with the guides being formed inthe area of the insulation-displacement contacts with recessed holdersfor the insulation-displacement contacts, and in which case the cablemanager can be matched to the plug connector housing.

Owing to the increasing bandwidth for data transmission intelecommunications and information technology, the conductors, contactsand conductor tracks have to be designed such that they are highlydefined with respect to one another, in order to comply with therequired values for the crosstalk attenuation.

This necessitates extremely tight tolerances, which can be complied withonly with difficulty during automated manufacturing processes.

The invention is thus based on the technical problem of providing amethod for matching an RF plug connector, in particular an RJ-45 femaleconnector, having at least one printed circuit board, with the printedcircuit board having contact points for RF contacts and contact pointsfor the insulation-displacement contacts, and with one contact point forthe RF contacts in each case being connected to a respective contactpoint for the insulation-displacement contacts, and a printed circuitboard which is suitable for this purpose and by means of which the RFcharacteristics can be adjusted within a narrow tolerance band.

The technical problem is solved by the subject matters with the featuresof patent claims 1 and 11. Further advantageous refinements of theinvention are described in the dependent claims.

For this purpose, at least one first conductor track, which is connectedon only one side to a contact point of an electrical contact, isarranged on the printed circuit board and, together with at least onesecond conductor track which is arranged on or in the printed circuitboard, forms a capacitor, with at least one frequency-dependentparameter of the arrangement being measured, the frequency-dependentparameter being compared with a nominal parameter, and the conductortrack with which contact is made on one side being partially removed orcut through as a function of the difference. This makes it possible toform a matchable capacitor using simple and cost-effective means, and bymeans of which the RF response of the arrangement can be matched. Theconductor tracks are in this case preferably connected to the contactpoints of the RF contacts, since this means that the matchingcapacitances are closer to the location of the source of the crosstalk.However, in principle, they may also be connected to the contact pointsof the insulation-displacement contacts, which are electricallyconnected to the contact points of the RF contacts. It should be notedthat, in principle, it is sufficient to cut through or to remove oneconductor track of a capacitor in order to change the capacitance.

The opposite electrode of the capacitor is preferably likewise formed bya conductor track that is connected to a contact point on one side.

In a further preferred embodiment, at least one further second conductortrack is arranged in an internal layer in the printed circuit board andis electrically connected to the conductor track on the printed circuitboard. This represents capacitances connected in parallel, so that thetotal capacitance is added, thus allowing the formation of asufficiently large capacitance on a relatively small area.

In a further preferred embodiment, at least two independent capacitorswhich are formed by conductor tracks are arranged on the printed circuitboard, in order to carry out symmetrical trimming with respect toground.

In a further preferred embodiment, the frequency-dependent parameter isdetermined and adjusted on the unpopulated printed circuit board. Thisis based on the knowledge that, particularly in the case of RF plugconnectors, the printed circuit board itself is responsible for themajority of the RF tolerances. These tolerances are generally geometrictolerances of the layout elements, such as conductor tracks, andtolerances of the dielectric constant of the material of the printedcircuit board. Automatic measurement on an unpopulated printed circuitboard is considerably easier than on a populated printed circuit board,or even on a printed circuit board that has been installed in a housing.The overall arrangement can thus be matched even at an early stage inthe process of producing the printed circuit board. The feed andmeasurement are in this case preferably provided centrally in solderedeyes of the contact points.

In a further preferred embodiment, only a portion of the estimatedconductor track shortening that is necessary is carried out in a firststep. The frequency-dependent parameter is then measured once again. Themeasured change is then used to determine the remaining conductor tracklength that is still to be removed or to be cut. This also takes accountof the tolerances relating to the conductor tracks in the matchingprocess. The conductor track shortening can in this case also besubdivided into more than two steps.

In a further preferred embodiment, the final cut during the cutting ofthe conductor track is carried out in a broader manner than the firstcut. This broader cut minimizes the capacitive influence of the cut partof the conductor track.

In a further preferred embodiment, the near crosstalk is determined asthe frequency-dependent parameter, thus making the matching processeasier, since the parameter to be optimized directly is determined, sothat there is no need for any further estimates of the influence of theparameter on the near crosstalk as would be the case, for example, withpure capacitance measurement.

The conductor track is preferably cut by means of a laser, preferably bymeans of a short-wave laser with a wavelength that is shorter than 600nm. The use of a laser for cutting the conductor track is extremelyfast, and can easily be automated. In principle, the conductor track canalso be cut or removed mechanically, for example by means of milling orelectrically by using an overcurrent to burn through it.

In a further preferred embodiment, the laser has an associated opticalpositioning system. This results in the conductor track being cut in amore defined manner, without any damage to closely adjacent conductortracks and without the conductor track to be cut not being cutcompletely.

During removal or cutting of the conductor track, it is possible forcopper particles to be deposited on the printed circuit board, and thesein turn reduce the resistance to overvoltages. The cutting or removal ofthe conductor track is thus preferably followed by a cleaning step toremove the copper particles and/or any other contamination.

The invention will be explained in more detail in the following textwith reference to a preferred exemplary embodiment. In the figure:

FIG. 1 shows an exploded illustration of a plug connector fortransmitting RF data (prior art),

FIG. 2 shows a printed circuit board for use in a plug connector shownin FIG. 1,

FIG. 3 shows a schematic equivalent circuit for the printed circuitboard,

FIG. 4 shows a schematic frequency response for the near crosstalk and

FIG. 5 shows a family of curves for the attenuation D of the nearcrosstalk as a function of the length of the conductor track to beremoved.

FIG. 1 shows an exploded illustration of a plug connector 1. The plugconnector 1 has a plug connector housing 2, a printed circuit board 3, ahold-down device 4 and a cable manager 5. The plug connector housing 2in the illustrated example is in the form of a female connector housingwith various latching and insertion means. The plug connector housing 2has a shielding plate 6 on the side surfaces. The printed circuit board3 is fitted on its front face with a first set of contacts 7, and isfitted on its rear face with a second set of insulation-displacementcontacts 8. One contact 7 in the first set is connected to a respectivecontact 8 in the second set. The printed circuit board 3 is theninserted into the plug connector housing 2. In the process, cylindricalpins 9 of the plug connector housing 2 pass through holes in the printedcircuit board 3, so that the plug connector housing 2 and the printedcircuit board 3 are adjusted and fixed with respect to one another. Thecontacts 7 (which are in the form of RF contacts) in the first set thenproject into an opening which is accessible from the front face of theplug connector housing. The hold-down device 4 is then pushed over thecontacts 8 in the second set, and is latched to the plug connectorhousing 2. For this purpose, the hold-down device 4 has latching tabs 10on the end face, and has openings 11 through it for theinsulation-displacement contacts 8. Furthermore, the hold-down device 4has two latching hooks 12, which are used for latching to the cablemanager 5.

FIG. 2 shows the unpopulated printed circuit board 3. The printedcircuit board 3 has eight contact points 21-28 and contact holes for theRF contacts, and eight contact points 31-38 for theinsulation-displacement contacts. The printed circuit board 3 also hasfurther plated-through holes 40 for connection of conductor tracks onthe front face and rear face and internal layers in the printed circuitboard, with the plated-through holes 40 being illustrated as smallcircles. The holes 41 in the printed circuit board 3 are in this caseillustrated as small squares. The conductor tracks which connect thecontact points 21-28 to their respectively associated contact point31-38 are not shown, with the exception of two parts of the contactpoints 24 and 35 since they are arranged on the rear face and/in theinternal layers of the printed circuit board. In addition to theelectrically connected conductor tracks between two contact points 21-28and 31-38, respectively, there are also four conductor tracks 43-46which are respectively connected on one side to a contact point 23-26.In this case, the two conductor tracks 44 and 46 form a capacitorbetween the contact points 24 and 26. In a corresponding way, the twoconductor tracks 43 and 45 form a capacitor between the contact points23 and 25. A further conductor track is preferably arranged in aninternal layer, is electrically connected to conductor track 44, and islocated under the conductor track 46. For circuitry purposes, thecontact points 21, 22; 23, 26; 24, 25 and 27, 28 and their respectivelyassociated contacts form a contact pair. In this case, the two outercontact pairs 21, 22 and 27, 28 are relatively uncritical with regard tonear crosstalk. The two inner and interleaved contact pairs 23, 26 and24, 25, on the other hand, are problematic. The capacitances which causedisturbances in this case are located between 23 and 24 as well asbetween 25 and 26, since the other couplings are negligible, owing tothe greater distances between them.

FIG. 3 shows the resultant equivalent circuit, including the schematictest layout. In this case, the capacitors C₄₆ and C₃₅ essentiallyrepresent capacitors formed by the conductor tracks 44 and 46 as well as43 and 45, respectively, while, in contrast, the capacitors C₃₄ and C₅₆,respectively, are formed by the adjacent contact points 23, 33 as wellas the associated conductor track, 24, 34 with the conductor track aswell as 25, 35 with the conductor track, and 26, 36 with the conductortrack. This bridge circuit can now be trimmed in order to force the nearcrosstalk below the required values. Before the trimming process, theasymmetry is first of all determined by determining the near crosstalkof one contact pair as a frequency-dependent parameter. In the presentcase, crosstalk is determined between the contact pair 23, 33 and 26, 36and the contact pair 24, 34; 25, 35. Since the measurement is preferablycarried out on the unpopulated printed circuit board 3, the contactpoints 33-36 are terminated with the correct impedance. The nearcrosstalk to the contact points 25, 24 is then measured, with RF signalsbeing injected into the contact points 23, 26, by means of a networkanalyzer which is symbolized in FIG. 3 by the frequency generator 50 andthe measurement device 51. The feeding and measurement of the RF signalsare in this case provided by means of a central contact in the soldereyes of the contact points 23-26.

FIG. 4 schematically shows the frequency response of the near crosstalkNEXT, with the profile a representing nominal near crosstalk, and theprofile b representing the measured actual near crosstalk for a measuredprinted circuit board. The nominal near crosstalk is determined, forexample, by means of a golden device. In this case, the measured nearcrosstalk is too high by an amount Δ NEXT, so that this must becompensated for by shortening the conductor tracks, thus reducing thecapacitance. The measure of how many millimeters of conductor trackcorrespond to what capacitance and thus to the near crosstalkattenuation D depends on the tolerances of the printed circuit board,such as the dielectric constant or the distance between the conductortracks. There is therefore no single straight line, but an entire familyof curves, as is illustrated schematically in FIG. 5. Since thetolerances are unknown, it may first of all be necessary to determinewhich curve is applicable to the printed circuit board to be matched.For this purpose, a piece of conductor track is first of all removed orcut through, and the measurements are then carried out once again. Theincrease in the attenuation D that is found can then be used todetermine the associated curve. If, on the other hand, the desiredattenuation is greater than that which can be achieved with the steepestcurve, the entire conductor track can be removed or cut through withoutany intermediate step. The method is then repeated on the othercapacitor.

The conductor track is preferably cut through by means of a short-wavelaser, whose power and focusing are matched to the copper track to becut such that, as far as possible, this is all that is removed. Theadvantage of a laser is its high speed with good reproducibility, sothat the matching process can easily be automated.

LIST OF REFERENCE SYMBOLS

-   1) Plug connector-   2) Plug connector housing-   3) Printed circuit board-   4) Hold-down device-   5) Cable manager-   6) Shielding plate-   7) Contacts-   8) Contacts-   9) Cylindrical pins-   10) Latching tabs-   11) Openings-   12) Latching hook-   21) Contact points (for RF contacts)-   22) Contact points (for RF contacts)-   23) Contact points (for RF contacts)-   24) Contact points (for RF contacts)-   25) Contact points (for RF contacts)-   26) Contact points (for RF contacts)-   27) Contact points (for RF contacts)-   28) Contact points (for RF contacts)-   31) Contact point (for an insulation-displacement contact)-   32) Contact point (for an insulation-displacement contact)-   33) Contact point (for an insulation-displacement contact)-   34) Contact point (for an insulation-displacement contact)-   35) Contact point (for an insulation-displacement contact)-   36) Contact point (for an insulation-displacement contact)-   37) Contact point (for an insulation-displacement contact)-   38) Contact point (for an insulation-displacement contact)-   40) Plated-through hole-   41) Hole-   43) Conductor track-   44) Conductor track-   45) Conductor track-   46) Conductor track-   50) Frequency generator-   51) Measurement device

1. A method for RF matching of an RF plug connector, having a printedcircuit board, with the printed circuit board having contact points forRF contacts and contact points for insulation-displacement contacts,with one contact point for the RF contacts in each case being connectedto a respective contact point for the insulation-displacement contacts,with the capacitive coupling, which causes near-end crosstalk, occurringbetween the RF contacts, wherein at least one first conductor track,which is connected on only one side to a contact point of an electricalcontact, is arranged on the printed circuit board and, together with atleast one second conductor track which is arranged on and/or in theprinted circuit board, forms a capacitor, with at least onefrequency-dependent parameter of the arrangement being measured, thefrequency-dependent parameter being compared with a nominal parameter,and the conductor track with which contact is made on one side beingpartially removed or cut through as a function of the difference.
 2. Themethod as claimed in claim 1, wherein the second conductor track is inthe form of a conductor track with which contact is made on one side. 3.The method as claimed in claim 1, wherein at least one further secondconductor track is arranged in an internal layer in the printed circuitboard and is connected to the second conductor track that is arranged onthe printed circuit board.
 4. The method as claimed in claim 1, whereinat least two matchable capacitors are arranged on the printed circuitboard.
 5. The method as claimed in claim 1, wherein thefrequency-dependent parameters are determined on the unpopulated printedcircuit board.
 6. The method as claimed in claimed claim 1, wherein in afirst step, only a portion of the estimated conductor track shorteningthat is necessary is carried out, the frequency-dependent parameter ismeasured once again, and the remaining conductor track length which isstill to be removed or to be cut is determined from this.
 7. The methodas claimed in claim 6, wherein, in the final step, the conductor trackis cut in a broader manner than in the first step.
 8. The method asclaimed in claim 1, wherein near crosstalk is determined as thefrequency-dependent parameter.
 9. The method as claimed in claim 1,wherein the conductor track is cut by means of a laser.
 10. The methodas claimed in claim 9, wherein the process of controlling the laser isassisted by means of an optical system.
 11. A printed circuit board forholding RF contacts and insulation-displacement contacts for an RF plugconnector, with the printed circuit board having eight contact pointsfor RF contacts and eight contact points for insulation-displacementcontacts, with one contact point for the RF contacts in each case beingconnected to a respective contact point for the insulation-displacementcontacts, and with capacitive coupling which causes near-end crosstalkoccurring between the RF contacts, wherein at least one first conductortrack, which is connected on only one side to a contact point of anelectrical contact, is arranged on the printed circuit board and,together with at least one second conductor track which is arranged onand/or in the printed circuit board, forms a capacitor.
 12. The printedcircuit board as claimed in claim 11, wherein the second conductor trackis likewise a conductor track which is connected to a contact point onone side.
 13. The printed circuit board as claimed in claim 11, whereinat least one further second conductor track is arranged in an internallayer in the printed circuit board and is connected to the furtherconductor track that is arranged on the printed circuit board.
 14. Theprinted circuit board as claimed in claim 11, wherein at least twomatchable capacitors are arranged on the printed circuit board.
 15. Theprinted circuit board as claimed in claim 11, wherein the firstcapacitor is arranged between the contact points, and the secondcapacitor is arranged between the contact points.